Cordelia's friend Aura is first seen in the series premiere of Buffy, Welcome to the Hellmouth (1997), in which the Buffyverse's first dead body, a boy bitten and drained by Darla, falls out of her gym locker. Aura is mentioned again in Prophecy Girl (1997).
This episode introduces phantom Dennis, who will be Cordelia's "roommate" for the next three years. Friendly with Cordelia's friends (She (2000)) and exhibiting caring feelings for Cordelia herself (Expecting (2000)), Dennis warns his roomie repeatedly about dangerous intruders (Five by Five (2000)).
Although BJ Porter appeared in Angel for just a few moments in only this episode (in the other ones Dennis is a friendly but invisible ghost), the shot of his face looking upward in despair was so powerful and moving that it remains in the opening credits through the rest of the series' run, including the final episode.
The flashback scenes take place in Los Angeles in 1946.